Freeze-thaw separation of solids from tar sands extraction effluents

ABSTRACT

THIS SPECIFICATION DISCLOSES TREATMENT OF WATER DISCHARGED FROM A HOT WATER PROCESS FOR SEPARATING BITUMEN FROM TAR SANDS. THE TREATMENT COMPRISES AGGLOMERATING CLAY DISPERSED IN THE WATER, ALTERNATELY FREEzING AND THAWING THE WATER INTO A SLUDGE LAYER AND A CLARIFIED WATER LAYER. THE CLARIFIED WATER LAYER IS SUBSTANTIALLY REDUCED IN CLAY CONTENT COMPARED TO THE WATER DISCHARGED FROM THE HOT WATER PROCESS AND IS SUITABLE FOR RECYCLE OR DISCARD.

Aug. 7, 1973 o. M. ELLIOTT 3,751,358

FREEZE-THAW SEPARATION OF SOLIDS FROM TAR SANDS EXTRACTION EFFLUENTSFiled Jan. 19, 1972 United States Patent 3 751,358 FREEZE-THAWSEPAitATION OF SOLIDS FROM TAR SANDS EXTRACTION EFFLUENTS Orrin M.Elliott, Media, Pa., assignor to Great Canadian Oil Sands, Limited,Toronto, Ontario, Canada Filed Jan. 19, 1972, Ser. No. 219,039

Int. Cl. Cg 1/04 U.S. Cl. 208-41 14 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a process for clarifying water discharged froma hot water process for separating bitumen from tar sands. It has beenfound that agglomeration followed by freezing and thawing can be appliedto clay and silt containing water discharges to produce a clarifiedwater suitable for recycle as at least a portion of the feed water tothe hot water process.

Numerous deposits of bituminous tar sands exist throughout the world.The most extensive deposits are found in northern Alberta, Canada. Thesands are composed of a siliceous materials, generally having a sizegreater than that passing a 325 mesh screen, saturated with a relativelyheavy, viscous bitumen in quantities of from 5 to 21 weight percent ofthe total composition. More typically, the bitumen content of the sandsis between about 8 to 15 percent. This bitumen is quite viscous andcontains typically 4.5 percent sulfur and 38 percent aromatics. Itsspecific gravity at 60 F. ranges typically from about 1.00 to about1.06. The tar sands also con tain clay and silt. Silt is defined asmineral which will pass a 325 mesh screen but which is larger than 2microns. Clay is mineral smaller than 2 microns including some siliceousmaterial of that size.

There are several well-known processes for effecting separation ofbitumen from the tar sands. In the hot water method, the bituminoussands are jetted with steam and mulled with a minor amount of hot waterat temperatures in the range of 140 to 210 F. The resulting pulp isconducted to a sump where it is diluted with additional hot water andcarried to a separation cell maintained at a temperature of about 150 to200 F. In the separation cell, sand settles to the bottom as tailingsand bitumen rises to the top in the form of an oil froth. An aqueousmiddlings layer containing some mineral and bitumen is formed betweenthese layers. A scavenger step may be conducted on the middlings layerfrom the primary separation step to recover additional amounts ofbitumen therefrom. This step usually comprises aerating the middlings astaught by K. A. Clark, The Hot Water Washing Method, Canadian Oil andGas Industries 3, 46 (1950). These froths can be combined, diluted withnaphtha and centrifuged to remove more water and residual mineral. Thenaphtha is then distilled off and the bitumen is coked to a high qualitycrude suitable for further processing.

The water discharged from the hot water process must be stored, disposedof or recycled back into the process. Because this water containsbitumen emulsions, finely dispersed clay with poor settlingcharacteristics and other contaminants, water pollution considerationsprohibit discarding the water into rivers, lakes or other natural bodiesof water. It has been proposed that the water be stored in evaporationponds but this proposal would involve large space requirements and theconstruction of expensive enclosure dikes. It has also been suggestedthat the water in the effluent discharge be recycled back into theprocess as an economic measure to conserve both heat and water. CanadianPat. 841,581, issued May 12, 1970 to Floyd et al., teaches that some ofthis water can be so recycled but that the amount of recycle is limitedby the dispersed silt and clay content of the water which can reducefroth yield by increasing the viscosity of the middlings layer andretarding the upward settling of bitumen flecks. A proportion of waterin the diluted tar sands pulp fed into the separation cell musttherefore be fresh waterwater which is substantially free of the clayand silt found in middlings water. In fact, with some high clay contenttar sands feeds, all of the water in the diluted pulp must be added asfresh water.

It has been found that water discharged from the process containing siltand clay can be made suitable for recycle as at least a portion of thehot water process water feed by treating the discharge according to amethod of agglomeration, freezing, thawing and filtration as describedherein. It is known that agglomeration by means such as flocculation,even with extended settling, cannot be used to clarify water from a hotwater process. Flocculation-settling produces sludges of less than 10weight percent solids from pondwater. It has been found by the presentinvention that agglomeration such as by flocculation, freezing andthawing produces solids compaction of greater than 10 weight percentsolids up to about 30 weight percent. It has also been found that properagglomeration of the pondwater must be combined with the freezing andthawing steps. Freezing and thawing alone will not produce a stablecompacted sludge of more than 10 weight percent solids.

Although the present invention is not to be bound by theoreticalexplanation, it is believed that the freezing and thawing sequencecauses solids compaction by concentration and compression of the clayagglomerates during the freezing step followed by settling of the largerand more dense agglomerates in the thawing step.

When pondwater is treated with an acid, or salts, the clay agglomerates.As freezing of the agglomerated clay slurry proceeds, ice crystals areformed thus compacting the clay among these crystals. This compactioncontinues until the sample is frozen solid. Upon thawing, the compactedagglomerates settle to the bottom of the container. Visual observationof the frozen treated pondwater has shown the existence of the twophases. The phases are randomly formed throughout the sample, one beingclear; the other opaque. This fact suggests that a clear liquid phaseand a sludge phase are being formed in the freezing step of theoperation. Another fact which is consistent with this concept is therelative size distribution of solids in pondwater before and aftertreatment by the freezthaw cycle. The mechanism postulated above wouldpredict that the particle sizes in the treated pondwater would be largerbecause of the concentration and compression of the solid during theprocess.

For the purpose of the present specification the term pondwater isdefined as eflluent discharge from a hot water process which efiluenthas been settled to give a composition comprising water containing up toabout 20 percent solids, between to percent of which is fine clay of asize smaller than 2 microns. The effluent discharge from a hot waterprocess comprises middlings material of depleted bitumen content whichhas undergone final treatment, the sand tailin-gs layer from the processand other discharged water-containing fractions which are not theprimary products of the hot water process. The discharge is removed fromthe process area as a slurry of about 25 to 60, typically 45, percentsolids by weight. The effiuent contains virtually all of the claymaterial which was present in the feed. Typically, the amount is 2 to 10weight percent of the feed. This material is smaller than 2 microns andhas extremely poor settling characteristics.

The present invention is describable as an improvement to the hot Waterprocess for treating bituminous tar sands in which the hot water processcomprises forming a mixture of tar sands and water, passing the mixtureinto a separation zone to form an upper bitumen froth layer, a middlingslayer comprising water, finely divided mineral and bitumen and a sandtailings layer. The improvement comprises agglomerating finely dividedminerals of at least a portion of the middlings, freezing the portioncontaining agglomerated finely divided minerals, thawing the portion andrecovering from said thawed portion a lower sludge layer characterizedby a substantially increased mineral content compared to the middlingsportion and an upper clarified water layer substantially reduced inmineral content and suitable for recycle back into the hot water processas at least a portion of the water utilized to form the mixture of tarsands and water.

The present invention can be described in more detail with reference tothe drawing which shows the present improvement in combination with apreferred embodiment of the hot water process.

In the figure, bituminous tar sands are fed into the system through line1 where they first pass to a conditioning drum or muller 3. Water andsteam are introduced from 2 and mixed with the sands. The total water sointroduced is a minor amount based on the weight of the tar sandsprocessed and generally is in the range of 10 to 45 percent by weight ofthe total mixture. Enough steam is introduced to raise the temperaturein the conditioning drum to within the range of 130 to 210 F. andpreferably to above 170 F. Monovalent alkaline reagents can also beadded to the conditioning drum, usually in amount of from 0.1 to 3.0pounds per ton of tar sand. The amount of such alkaline reagentpreferably is regulated to maintain the pH of the middlings layer inseparator zone 12 within the range of 7.5 to 9.0. Best results areobtained at a pH value of 8.0 to 8.5. The amount of the alkaline reagentthat needs to be added to maintain a pH value in the range of 7.5 to 9.0may vary from time to time as the composition of the tar sands asobtained from the mine site varies. The best alkaline reagents to usefor this purpose are caustic soda, sodium, carbonate or sodium silicate,although any of the other monovalent alkaline reagents can be used ifdesired.

Mulling of the tar sands produces a pulp which then passes from theconditioning drum as indicated by line 4 to a screen indicated at 5. Thepurpose of screen 5 is to remove from the tar sand pulp any debris,rocks or oversized lumps as indicated generally at 6. The pulp thenpasses from screen 5 as indicated by 7 to a sump 8 where it is dilutedwith additional water from 9 and a middlings recycle stream 10. In theevent the clay content of the tar sands is high, a relatively high rateof fresh or treated feed water introduction through 9 can be employed tocompensate for the high clay introduction while a correspondingly highrate of transfer of middlings layer through line 15 as hereinafterdescribed can be maintained. Under these circumstances recycling of ofthe other stream of middlings through line 10 to the sump is notrequired.

Modifications that may be made in the process as above described includesending a minor portion of the middlings recycle stream from line 10through a suitable line (not shown) to the conditioning drum 3 to supplyall or a part of the water needed therein other than that suppliedthrough condensation of the stream which is consumed. Also, if desired,a stream of the middlings recycle can be introduced onto the screen 5 toflush the pulp therethrough and into the sump. As a general rule, thetotal amount of water added to the natural bituminous sands as liquidwater and as steam prior to the separation step should be in the rangeof 0.2 to 3.0 tons per ton of the bituminous sands. The amount of waterneeded within this range increases as the silt and clay content of thebituminous sand increases. For example, when 15 percent by weight of themineral mattter of the tar sands has a particle size below 4-4 microns,the fresh water added generally can be about 0.3 to 0.5 ton per ton oftar sands. On the other hand, when 30 percent of the mineral matter isbelow 44 microns diameter, generally 0.7 to 1.0 ton of water should beused per ton of tar sands. Correspondingly the amount of bitumen-richmiddlings removed through line 15 will vary depending upon the rate offresh water addition. As a general rule, the rate of withdrawal ofbitumen-rich middlings to scavenger zone 16 will be 10 to 75 gallons perton of tar sands processed when 15 percent by weight of the mineralmatter is below 44 microns and to 250 gallons per ton when from 25 to 30percent of the mineral is of this fine particle size.

Further following the process, the pulped and diluted tar sands arepumped from the sump through line 11 into the separation zone 12. Thiszone comprises a cell which contains a relatively quiescent body of hotwater. In the cell, the diluted pulp forms into a bitumen froth layerwhich rises to the cell top and is withdrawn via line 13 and a sandtailings layer which settles to the bottom to be withdrawn through line14. An aqueous middlings layer between the froth and tailings containssilt and clay and some bitumen which failed to form froth. In order toprevent the buildup of clay in the system, it is necessary tocontinually remove some of the middlings layer and supply enough waterin the conditioning operations to compensate for that so removed. Therate at which the middlings need to be removed from the system dependsupon the content of clay and silt present in the tar sands feed and thiswill vary from time to time as the content of these fines varies. If theclay and slit content is allowed to build up in the system, theviscosity of the middlings layer will increase. Concurrently with suchincrease, an increase in the proportions of both the bitumen and thesand retained by the middlings will occur. If the clay and silt contentis allowed to build up too high in the system, effective separation nolonger will occur and the process will become inoperative. This can beavoided by regulating the recycling and withdrawal of middlings andinput of fresh water per the invention disclosed and claimed in theFloyd et al. patent. However, even when the seperation step is operatingproperly, the middlings layer withdrawn through line 15 will contain asubstantial amount of bitumen which did not separate. Hence themiddlings layer withdrawn through line 15 is, for purpose ofdescription, herein referred to as oil-rich or bitumenrich middlings.

The oil-rich middlings stream withdrawn from separator 12 through line15 is sent to a scavenger zone 16 wherein an air flotation operation isconducted to cause the formation of additional bitumen froth. Theprocessing conducted in the scavenger zone 16 involves air flotationprocedures conventionally utilized in processing of ores. This involvesproviding a controlled zone of aeration in the flotation cell at a locuswhere agitation of the middlings is being effected so that air becomesdispersed in the middlings in the form of small bubbles. The drawingillustrates a flotation cell of the subaeration type wherein a motorizedrotary agitator is provided and air is fed thereto in controlled amount.Alternatively the air can be fed in through the shaft of the rotor. Therotor effects entraining of the air in the middlings. This air causesthe formation of additional bitumen froth which passes from thescavenger zone 16 through line 17 to a froth settler zone 18. Abitumen-lean middlings stream is removed from the bottom of thescavenger zone 16 via line 19.

In the settler zone 18, the scavenger froth forms into a lower layer ofsettler trailings which is withdrawn and recycled via line 20 to bemixed with bitumen-rich middlings for feed to the scavenger zone 16 vialine 15. In

the settler zone, an upper layer of upgraded bitumen froth forms abovethe tailings and is withdrawn through line 21 and is mixed with primaryfroth in line 13. The combined froths are at a temperature of about 160F. They are heated with steam and diluted with suflicient naphtha or 6treated before recycle into sump 8 for dilution of the tar sands pulp.

The drawing shows the present invention applied to pondwater in a singlezone. If desired the pondwater can be removed from the pond andagglomerated, frozen and other diluent from 22 to reduce the viscosityof the bi- 5 thawed and settled in separate zones. tumen forcentrifuging in zone 23 to produce a bitumen The agglomeration step onthe pondwater can be product 24 suitable for further processing. carriedout by adding a convent onal agglomeratlng rea- The oil-lean middlingsin line 19 and the sand tailings gent to th ater with gentle agltahomAmong h vlanfrom the separation zone 12 are combined to form an ousreagents useful for agglomeratlng clay are sodium effiuent dischargewhich is delivered via line 25 to a sand and calcium chlorides, alumlnumsulfate (alum), poly- P Zone 26 Via distiibntion P p The eillnentalkylene oxides such as polyethylene oxide, compounds tains between 25and 60 weight percent sand and silt maof calcium such as calciumhydroxide, calcium oxide, terial which is larger than about 2 microns.The distribucalcium chloride, calcium nitrate, calcium acid phosphate,tion p p Provides iiol continuous and uniform de l y calcium sulfate,calcium tartrate, calclum citrate, calcium f t eihnent to the send PZones Where the sand and sulfonate, calcium lactate, the calcium salt ofethylene d1- silt material is deposited- The Water in the eillnent iamine tetraacetate and similar organic sequestering agents. chargepercolates d through and over the sand P Also suitable are guar flour ora high molecular weight zone t0 the pond Z0116 28 where it collects 3SpOIldac ylamide olymer such as polyacrylam de or a co. Water containingn to about 12 Weight Percent suspended polymer of acrylamide and acopolymerizable carboxylic Solids, between 80 to 100 Percent of which isa tine clay acid such as acrylic acid. Additional flocculants include Ofa size smaller than 2 microns. The pondwater also 6011- the polymers ofacrylic or methacrylic acid derivatives tains between ab and WeightPeioent bitumenfor example, acrylic acid, methacrylic acid, the alkaliBecause of the Particnlar composition of this Pondwater, metal andammonium salts of acrylic acid or methacrylic and especially because ofthe extreme fineness of the susid, i id methaeryiamide, h aminoalkylaerypended y material which has extremely P settling lates, theaminoalkyl acrylamides, the aminoalkyl methoharaetetisties, the Watercannot be discarded to y acrylamides and the N-alkyl substitutedaminoalkyl esters great extent recycled back into the hot water system.f ith acrylic o1- methacrylic acids. 1

The Present invention is pp to this p i Preferably agglomeration isaccomplisehd by changing clarifying the Water y back to be mixed W the30 the pH of the water. Variation of pH causes a change in Process sendsieed- Preferably the Process is e011 the charge on the edges of the clayparticles, thus allowdnoted byintlodnoing agglomefating agents into theP ing agglomeration. The efiluent discharge from the hot Water followedy altefnetely freezing and thawing the water process has a pH rangingfrom about 7.5 to 9.0 Water in the P Zone- In the Present invention,typically about 8.3. In this range, the contained mineral creased solidscompaction is obtained by one frezing-thawmaterial is not agg1emerate ii the pH above about ing cycle of agglomerated pondwater; however. it isp 9.0 or lowering it below about 7.5 causes agglomeration. ferred thatthe freezing and thawing be conducted in a More preferably,agglomeration in one acoomplurality of cycles since it has been foundthat the amount phshed by adding lf i acid (to the middlings or OfSOlidS compaction is a function of the number Of freezefluent dischargeportion as the case may be) to about PH 5. thaw oyoles Petfonned- Thefreezing and thawing steps can be conducted by Through alternateffeezings and thawing steps the P any means known in the art. Preferablyhowever, freezing water settles into a sludge at the bottom of the pondand d thawing of h pondwater i conducted i the d sets a clarified waterPOI'tiOIl near the pond surface. The zone by dividing the zone into twoareas, The first area sludge contains about 30 Weight Percent solids andthe is allowed to freeze by exposure to ambient temperatures pondwateris reduced in solids content to the extent that it below 32 Water beingdischarged f om the distrihu. is suitable y Vie line 29 back to line 9as a P tion pipes through the sand zone collects in a second pond tionof the Water used to form the nliXtnIe of Weter and area. During periodswhen the ambient temperatures are tar sands Passed into the separationCell greater than 32 F., the clear clarified water from the The treatedWater can be introduced Via line 29 into first area is discarded orrecycled. The water in the second the system as all a Portion of theWater in line 9 to the area is diverted to the first along with currentrunofl? from snnlP as shown can be altetnetively introduced into the thedistributed pipes. This pondwater is collected until system via lines 210 as a screen Wash at y again average ambient temperature falls below32 F. tiesil'ed Point of introduction into the P Another approach is toalternatively add warm water Although the invention has been described pWith at various ends of a frozen pond at certain intervals overreference to the treatment of Pendwater from the hot a period when theambient temperature is below 32 F. water process effluent discharge, itshould be pointed out Thi approach results i repeated free i and h ithat the invention can be practiced on y Water stream settling cycles.Another method of conducting the freezfrom the Separation ceil- Forexample, referring again t ing-thawing-settling technique of the presentinvention is to the drawing, the bitumen-lean iddlings line 19 fromcirculate water from beneath frozen pondwater to the sure flotationcavenger Zone 16 can be directly treated by face of the ice accompaniedby addition of additionl runthe invention to make these middlingssuitable for recycle of]? w te either to beneath 0 onto th surface f h iback into the process. Also the middlings in line 10 can be Thefollowing examples illustrate the invention:

TABLE I Reagent dosage, Feed, wt. Sludge, pounds/1,000 gallons percentWt. per- Reagent clay cent clay Clear Cloudy Note Anson 13:3 it; 131323?, FeCl 6. 5 13. 0 7.14 a. s @8012 123g 8' 2:? H H2804 "i 0: 23:2 if?g ifi None 6. 6.5

1 Intermediate dosages not tested. Clear" indicates sample settledWithin 1 hour to produce clear supernatant. Oloudy" supernatants did notsettle further within 1 week. Cloudy" supernatants contained 200 p.p.m.suspended solids (by visual inspection).

2 Supernatant settled clear within 48 hours.

Several freeze-thaw runs on pondwater from a hot water process forseparating bitumen from tar sands are reported in Tables I and II. InTable I pondwater feeds of various weight percent clays were treatedwith various agglomerating agents, then frozen, thawed and settled andcompared to an untreated sample. The results in Table I indicate thatvarious agglomerating agents can be used in the present invention andthat the process of the present invention is applicable to theclarification of pondwaters of various clay compositions.

The runs in Table II were made on pondwater containing 6.5 weightpercent clay to determine the extent of sludge compaction for repeatedfreeze-thaw cycles. These runs show that it is possible to achievecompactions of 30 weight percent solids by using the process of thepresent invention.

TABLE II Weight percent solids in sludge Test 1, 5.05 Test 2, 5.05 Test3, 13.8

pounds pounds pounds Freeze-thaw cycles HgSOq/LOOO HzSOq/LOUO A12(SO4)3/completed gallons gallons 1,000 gallons The embodiments of the inventionin which an exclusive property or privilege is claimed are defined asfollows:

1. -In a hot water process for treating bituminous tar sands whichcomprises: forming a mixture of tar sands and water; passing saidmixture into a separation zone to form an upper bitumen froth layer, amiddlings layer comprising water, finely divided mineral and bitumen anda sand tail-ings layer; and separately removing said bitumen frothlayer, middlings layer and tailings layer; the improvement whichcomprises:

(a) agglomerating finely divided mineral of at least a portion of themiddlings;

(b) freezing the portion of middlings containing agglomerated finelydivided mineral; I

(c) thawing the frozen middlings portion and (d) recovering from athawed portion a lower sludge layer characterized by a substantiallyincreased mineral content compared to said middlings portion and anupper clarified water layer substantially reduced in mineral content.

2. The process of claim 1 in which the agglomerating step comprisesadding an agglomerating agent to agglomerate said mineral component.

'3. The process of claim 1 in which the agglomeration step comprisesadjusting the pH of said middlings portion below about 7.5.

4. The process of claim 1 in which the agglomeration step comprisesadjusting the pH of said middlings portion to above about 9.0.

5. The process of claim 1 in which said Water layer substantiallyreduced in mineral content is recycled back into the hot water processas at least a portion of the water utilized to form said mixture of tarsands and water.

6. The process of claim 1 in which said freezing and thawing steps arerepeated.

7. The process of claim 1 in which said lower sludge layer of step (d)comprises greater than 10 weight percent solids.

8. In the hot water process for treating bituminous tar sands whichcomprises: forming a mixture of bituminous sands and water; passing themixture to a separation zone to form an upper bitumen froth layer, amiddlings layer comprising water, clay and some bitumen and a sandtailings layer; recovering said froth layer; and passing at least aportion of the middlings layer and tailings layer to a settling pondzone; the improvement which comprises:

(a) agglomerating the clay in at least a portion of the water containedin said settling pond zone;

(b) freezing said portion containing agglomerated fine- 1y dividedmineral;

(c) thawing said frozen portion and (d) recovering from said thawedportion a lower sludge layer characterized by a substantially increasedmineral content compared to said middlings portion and an upperclarified water layer substantially reduced in mineral content andsuitable for recycle back into the hot water process as at least aportion of the water utilized to form said mixture of tar sands andwater.

9. The process of claim 8 in which the agglomeration step comprisesadding an agglomerating agent to agglomerate said mineral component.

10. The process of claim 8 in which the agglomeration step comprisesadjusting the pH of said middlings portion below about 7.5.

11. The process of claim 8 in which the agglomeration step comprisesadjusting the pH of said middlings portion to above about 9.0.

12. The process of claim 8 in which said water layer substantiallyreduced in mineral content is recycled back into the hot water processas at least a portion of the water utilized to form said mixture of tarsands and; water.

13. The process of claim 8- in which said freezing and thawing steps arerepeated.

14. The process of claim 8 in which said lower sludge layer of step (d)comprises greater than 10 weight percent solids.

References Cited UNITED STATES PATENTS 3,526 ,5- 9/1970 Camp 208-113,314,881 4/1967 Tuwiner 2l060 CURTIS R. DAVIS, Primary Examiner US. Cl.X.R.

